1. Field of the Invention
This invention relates to biomaterials excellent in biocompatibility comprising composite materials of N-acylchitosans and collagens and a process for the production thereof and more particularly, it is concerned with biomaterials which can be applied to wound dressing materials, vascular prostheses, artificial skins, hemostatic agents, etc. and a process for the production thereof.
2. Description of the Prior Art
Chitosan is a composite polysaccharide consisting of N-acetyl-D-glucosamine and D-glucosamine, obtained by deacetylation of chitin with a concentrated alkali, in which the ratio of N-acetyl-D-glucosamine and D-glucosamine varies with the degree of the deacetylation as well known in the art.
Collagen is a material that is very excellent in biocompatibility, because it is a predominant component of the connective tissue and most suitable as an extracellular matrix. Collagen has widely been used as cosmetics or biomaterials, since it has a relatively low antigenecity although in the implantation between different species, there arises a problem of antigenecity because of being a protein. A product having a very low antigenecity called atelocollagen, which product is obtained by treating tropocollagen (collagen molecule) with a proteolytic enzyme except collagenase and removing the nonhelix part (telopeptide) at the terminal of the molecule is known. This atelocollagen has significant features, i.e. the best biocompatibility of the biomaterials which have been commonly used up to the present time, because of its low antigenecity, but the range of its use is limited since when applied to a living body, collagen is absorbed by the living body in due course and is more expensive than chitosan.
A composite material of chitosan and collagen has been proposed so as to make the best use of the features of chitosan and collagen and to compensate the disadvantages thereof (U.S. Pat. No. 4,378,017). When chitosan is applied to a living body as is, however, more foreign body reactions take place as compared with collagen and a number of giant cells are found around chitosan by an optical microscope, because chitosan is a polysaccharide not present in living bodies and apparently is a foreign body to living bodies. Therefore, it is difficult to make use of chitosan alone as a biomaterial and the method of improving the biocompatibility of chitosan by adding collagen is still insufficient, so that chitosan is not put to clinical and practical use.